1. Field of the Invention
The invention relates in general to a fabricating method of a wafer structure, and more particularly to a fabricating method of an oxidation-resistant wafer structure.
2. Description of the Related Art
Referring to FIG. 1, cross-sectional view of a conventional wafer structure is shown. Conventional wafer structure 10 includes a wafer 11, a conductive structure, an organic protective layer 13, an under bump metallurgy layer (UBM layer) 14 and a conductive bump 15. The conductive structure, a pad 12 for example, is positioned on the surface of the wafer 11. The organic protective layer 13 covers the wafer 11 and part of the pad 12 to expose the surface of the pad 12. The UBM layer 14 is connected to the surface of the pad 12 to enhance the surface bonding between the conductive bump 15 and the pad 12. The conductive bump 15, which is formed on the UBM layer 14, is made of lead-tin alloy with a lead/tin ratio of 95/5 or 97/3.
However, the surface of the high lead bump is easily oxidized to form an oxide layer on the surface of the bump. When the bump is bonded to an external component such as a substrate or a circuit board, the cold joint would easily occur, resulting in poor soldering of the product.